The intergalactic medium thermal history at redshift z=1.7--3.2 from the Lyman alpha forest: a comparison of measurements using wavelets and the flux distribution

We investigate the thermal history of the intergalactic medium (IGM) in the redshift interval z=1.7--3.2 by studying the small-scale fluctuations in the Lyman alpha forest transmitted flux. We apply a wavelet filtering technique to eighteen high resolution quasar spectra obtained with the Ultraviolet and Visual Echelle Spectrograph (UVES), and compare these data to synthetic spectra drawn from a suite of hydrodynamical simulations in which the IGM thermal state and cosmological parameters are varied. From the wavelet analysis we obtain estimates of the IGM thermal state that are in good agreement with other recent, independent wavelet-based measurements. We also perform a reanalysis of the same data set using the Lyman alpha forest flux probability distribution function (PDF), which has previously been used to measure the IGM temperature-density relation. This provides an important consistency test for measurements of the IGM thermal state, as it enables a direct comparison of the constraints obtained using these two different methodologies. We find the constraints obtained from wavelets and the flux PDF are formally consistent with each other, although in agreement with previous studies, the flux PDF constraints favour an isothermal or inverted IGM temperature-density relation. We also perform a joint analysis by combining our wavelet and flux PDF measurements, constraining the IGM thermal state at z=2.1 to have a temperature at mean density of T0/[10^3 K]=17.3 +/- 1.9 and a power-law temperature-density relation exponent gamma=1.1 +/- 0.1 (1 sigma). Our results are consistent with previous observations that indicate there may be additional sources of heating in the IGM at z<4.Comment: 15 pages, 14 figures, matches version accepted for publication on MNRA

Thermal constraints on the reionisation of hydrogen by population-II stellar sources

Measurements of the intergalactic medium (IGM) temperature provide a potentially powerful constraint on the reionisation history due to the thermal imprint left by the photo-ionisation of neutral hydrogen. However, until recently IGM temperature measurements were limited to redshifts 2 < z < 4.8, restricting the ability of these data to probe the reionisation history at z > 6. In this work, we use recent measurements of the IGM temperature in the near-zones of seven quasars at z ~ 5.8 - 6.4, combined with a semi-numerical model for inhomogeneous reionisation, to establish new constraints on the redshift at which hydrogen reionisation completed. We calibrate the model to reproduce observational constraints on the electron scattering optical depth and the HI photo-ionisation rate, and compute the resulting spatially inhomogeneous temperature distribution at z ~ 6 for a variety of reionisation scenarios. Under standard assumptions for the ionising spectra of population-II sources, the near-zone temperature measurements constrain the redshift by which hydrogen reionisation was complete to be z > 7.9 (6.5) at 68 (95) per cent confidence. We conclude that future temperature measurements around other high redshift quasars will significantly increase the power of this technique, enabling these results to be tightened and generalised.Comment: 15 pages, 8 figures, accepted for publication in MNRA

Improved measurements of the intergalactic medium temperature around quasars: possible evidence for the initial stages of He II reionization at z ≃ 6

We present measurements of the intergalactic medium (IGM) temperature within ∼5 proper Mpc of seven luminous quasars at z ≃ 6. The constraints are obtained from the Doppler widths of Lyα absorption lines in the quasar near zones and build upon our previous measurement for the z = 6.02 quasar SDSS J0818+1722. The expanded data set, combined with an improved treatment of systematic uncertainties, yields an average temperature at the mean density of log(T_0/K) = 4.21±^(0.03)_(0.03)(±^(0.06)_(0.07)) at 68 (95) per cent confidence for a flat prior distribution over 3.2 ≤ log (T_0/K) ≤ 4.8. In comparison, temperatures measured from the general IGM at z ≃ 5 are ∼0.3 dex cooler, implying an additional source of heating around these quasars which is not yet present in the general IGM at slightly lower redshift. This heating is most likely due to the recent reionization of He ii in vicinity of these quasars, which have hard and non-thermal ionizing spectra. The elevated temperatures may therefore represent evidence for the earliest stages of He ii reionization in the most biased regions of the high-redshift Universe. The temperature as a function of distance from the quasars is consistent with being constant, log (T_0/K) ≃ 4.2, with no evidence for a line-of-sight thermal proximity effect. However, the limited extent of the quasar near zones prevents the detection of He III regions larger than ∼5 proper Mpc. Under the assumption that the quasars have reionized the He II in their vicinity, we infer that the data are consistent with an average optically bright phase of duration in excess of 10^(6.5) yr. These measurements represent the highest redshift IGM temperature constraints to date, and thus provide a valuable data set for confronting models of H I reionization

The SLUGGS Survey: stellar kinematics, kinemetry and trends at large radii in 25 early-type galaxies

Due to longer dynamical time-scales, the outskirts of early-type galaxies retain the footprint of their formation and assembly. Under the popular two-phase galaxy formation scenario, an initial in situ phase of star formation is followed by minor merging and accretion of ex situ stars leading to the expectation of observable transitions in the kinematics and stellar populations on large scales. However, observing the faint galactic outskirts is challenging, often leaving the transition unexplored. The large-scale, spatially resolved stellar kinematic data from the SAGES Legacy Unifying Galaxies and GlobularS (SLUGGS) survey are ideal for detecting kinematic transitions. We present kinematic maps out to 2.6 effective radii on average, kinemetry profiles, measurement of kinematic twists and misalignments, and the average outer intrinsic shape of 25 SLUGGS galaxies. We find good overall agreement in the kinematic maps and kinemetry radial profiles with literature. We are able to confirm significant radial modulations in rotational versus pressure support of galaxies with radius so that the central and outer rotational properties may be quite different. We also test the suggestion that galaxies may be more triaxial in their outskirts and find that while fast rotating galaxies were already shown to be axisymmetric in their inner regions, we are unable to rule out triaxiality in their outskirts.We compare our derived outer kinematic information to model predictions from a two-phase galaxy formation scenario. We find that the theoretical range of local outer angular momentum agrees well with our observations, but that radial modulations are much smaller than predicted

A consistent determination of the temperature of the intergalactic medium at redshift z=2.4

We present new measurements of the thermal state of the intergalactic medium (IGM) at z∼2.4 derived from absorption line profiles in the Lyα forest. We use a large set of high-resolution hydrodynamical simulations to calibrate the relationship between the temperature-density (T--Δ) relation in the IGM and the distribution of HI column densities, NHI, and velocity widths, bHI, of discrete Lyα forest absorbers. This calibration is then applied to the measurement of the lower cut-off of the bHI--NHI distribution recently presented by Rudie et al. (2012). We infer a power-law T--Δ relation, T=T0Δγ−1, with a temperature at mean density, T0=[1.00+0.32−0.21]×104K and slope (γ−1)=0.54±0.11. The slope is fully consistent with that advocated by the analysis of Rudie et al (2012); however, the temperature at mean density is lower by almost a factor of two, primarily due to an adjustment in the relationship between column density and physical density assumed by these authors. These new results are in excellent agreement with the recent temperature measurements of Becker et al. (2011), based on the curvature of the transmitted flux in the Lyα forest. This suggests that the thermal state of the IGM at this redshift is reasonably well characterised over the range of densities probed by these methods

The impact of temperature fluctuations on the large-scale clustering of the Lyα forest

We develop a semi-analytic method for assessing the impact of the large-scale IGM temperature fluctuations expected following He ii reionization on three-dimensional clustering measurements of the Lyα forest. Our methodology builds upon the existing large volume, mock Lyα forest survey simulations presented by Greig et al. by including a prescription for a spatially inhomogeneous ionizing background, temperature fluctuations induced by patchy He ii photoheating and the clustering of quasars. This approach enables us to achieve a dynamic range within our semi-analytic model substantially larger than currently feasible with computationally expensive, fully numerical simulations. The results agree well with existing numerical simulations, with large-scale temperature fluctuations introducing a scale-dependent increase in the spherically averaged 3D Lyα forest power spectrum of up to 20–30 per cent at wavenumbers k ∼ 0.02 Mpc− 1. Although these large-scale thermal fluctuations will not substantially impact upon the recovery of the baryon acoustic oscillation scale from existing and forthcoming dark energy spectroscopic surveys, any complete forward modelling of the broad-band term in the Lyα correlation function will none the less require their inclusion

A new mechanical stellar wind feedback model for the Rosette Nebula

The famous Rosette Nebula has an evacuated central cavity formed from the stellar winds ejected from the 2–6 Myr old codistant and comoving central star cluster NGC 2244. However, with upper age estimates of less than 110 000 yr, the central cavity is too young compared to NGC 2244 and existing models do not reproduce its properties. A new proper motion study herein using Gaia data reveals the ejection of the most massive star in the Rosette, HD 46223, from NGC 2244 occurred 1.73 (+0.34, −0.25) Myr (1σ uncertainty) in the past. Assuming this ejection was at the birth of the most massive stars in NGC 2244, including the dominant centrally positioned HD 46150, the age is set for the famous ionized region at more than 10 times that derived for the cavity. Here, we are able to reproduce the structure of the Rosette Nebula, through simulation of mechanical stellar feedback from a 40 Mₒ star in a thin sheet-like molecular cloud. We form the 135 000 Mₒ cloud from thermally unstable diffuse interstellar medium (ISM) under the influence of a realistic background magnetic field with thermal/magnetic pressure equilibrium. Properties derived from a snapshot of the simulation at 1.5 Myr, including cavity size, stellar age, magnetic field, and resulting inclination to the line of sight, match those derived from observations. An elegant explanation is thus provided for the stark contrast in age estimates based on realistic diffuse ISM properties, molecular cloud formation and stellar wind feedback

Heating and ionization of the primordial intergalactic medium by high mass x-ray binaries

We investigate the influence of high-mass X-ray binaries (HMXBs) on their high-redshift environments. Using a one-dimensional radiative transfer code, we predict the ionization and temperature profiles surrounding a coeval stellar population, composed of main-sequence stars and HMXBs, at various times after its formation. We consider both uniform density surroundings, and a cluster embedded in a 108 M⊙ Navarro–Frenk–White (NFW) halo. HMXBs in a constant density environment produce negligible enhanced ionization because of their high-energy spectral energy distributions and short lifetimes. In this case, HMXBs only marginally contribute to the local heating rate. For NFW profiles, radiation from main-sequence stars cannot prevent the initially ionized volume from recombining since it is unable to penetrate the high-density galactic core. However, HMXB photons stall recombinations behind the front, keeping it partially ionized for longer. The increased electron density in these partially ionized regions promotes further cooling, resulting in lower intergalactic medium (IGM) temperatures. In the context of this starburst model, we have shown that HMXBs do not make a major contribution to reionization or IGM heating. However, X-ray escape fractions are high in both density profile cases. Continuous star formation may result in the build up of X-rays over time, reducing the ionization time-scale and potentially leading to low level ionization of the distant IGM

Abundance ratios and IMF slopes in the dwarf elliptical galaxy NGC 1396 with MUSE

Deep observations of the dwarf elliptical (dE) galaxy NGC 1396 (MV = −16.60, Mass ~4 × 10^8 M�), located in the Fornax cluster, have been performed with the VLT/ MUSE spectrograph in the wavelength region from 4750 − 9350 Å. In this paper we present a stellar population analysis studying chemical abundances, the star formation history (SFH) and the stellar initial mass function (IMF) as a function of galacto-centric distance. Different, independent ways to analyse the stellar populations result in a luminosity-weighted age of ∼ 6 Gyr and a metallicity [Fe/H]∼ −0.4, similar to other dEs of similar mass. We find unusually overabundant values of [Ca/Fe] ∼ +0.1, and under-abundant Sodium, with [Na/Fe] values around −0.1, while [Mg/Fe] is overabundant at all radii, increasing from ∼ +0.1 in the centre to ∼ +0.2 dex. We notice a significant metallicity and age gradient within this dwarf galaxy. To constrain the stellar IMF of NGC 1396, we find that the IMF of NGC 1396 is consistent with either a Kroupa-like or a top-heavy distribution, while a bottom-heavy IMF is firmly ruled out. An analysis of the abundance ratios, and a comparison with galaxies in the Local Group, shows that the chemical enrichment history of NGC 1396 is similar to the Galactic disc, with an extended star formation history. This would be the case if the galaxy originated from a LMC-sized dwarf galaxy progenitor, which would lose its gas while falling into the Fornax cluster

The effect of intergalactic helium on hydrogen reionisation: implications for the sources of ionising photons at z > 6

We investigate the effect of helium on hydrogen reionisation using a hydrodynamical simulation combined with the cosmological radiative transfer code CRASH. The simulations are run in a 35.12/h comoving Mpc box using a variety of assumptions for the amplitude and power-law extreme-UV (EUV) spectral index, alpha, of the ionising emissivity. We use an empirically motivated prescription for ionising sources which ensures all of the models are consistent with constraints on the Thomson scattering optical depth and the hydrogen photo-ionisation rate at z=6. The inclusion of helium slightly delays reionisation due to the small number of ionising photons which reionise neutral helium instead of hydrogen. However, helium has a significant impact on the thermal state of the IGM. Models with alpha=3 produce IGM temperatures at the mean density at z=6 which are about 20 % higher compared to models without helium photo-heating. Harder EUV indices produce even larger IGM temperature boosts. A comparison to recent observational estimates of the IGM temperature at z=5 - 6 suggests that hydrogen reionisation was primarily driven by pop-II stellar sources with a soft EUV index, alpha<3. We also find that faint, as yet undetected galaxies, characterised by a luminosity function with a steepening faint-end slope and an increasing Lyman continuum escape fraction (fesc=0.5), are required to reproduce the ionising emissivity used in our simulations at z>6. Finally, we note there is some tension between recent observational constraints which indicate the IGM is > 10% neutral by volume z=7, and estimates of the ionising emissivity at z=6 which indicate only between 1 and 3 ionising photons are emitted per hydrogen atom over a Hubble time. This tension may be alleviated by either a lower neutral fraction at z=7 or an IGM which still remains a few % neutral by volume at z=6.Comment: 19 pages, 12 figures; MNRAS in pres